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The Aerodynamic Performance Study on Small Wind Turbine with

500W Class through Wind Tunnel Experiments

Ho Seong JI1†, Joon Ho BAEK 2, Rinus MIEREMET2, Kyung Chun KIM3

1† MEMS Technology Center, Pusan National University, Busan, 609-735, Republic of KOREA

([email protected] ) 2 Department of Engineering Research, ESCO RTS, Daejeon, Republic of Korea

3 School of Mechanical Engineering, Pusan National University, Busan, 609-735, Republic of KOREA

Abstract: - For urban usage of an Archimedes spiral horizontal axis wind turbine, the aerodynamic

characteristics including output power, power coefficient, and effect of the angle of attack was

investigated using proto-type wind turbine model with Archimedes spiral shape. To provide the

aerodynamic performance, the experimental model was consisted with Archimedes spiral wind turbine

model, torque meter, powder brake with PWM (Pulse Width Modulation) control basic and RPM

sensor. The power coefficient as a function of tip speed ratio with more than 85% of Betz limit can be

observed successfully. The Archimedes spiral wind turbine model employed in this study shows the

similarity with Modern multiblade turbine type. And the maximum power coefficient as a function of

the TSR shows the similar that of Ideal Efficiency of Propeller-type turbine. Through the experiments

on the angle of attack change, the fundamental information for the automatic yawing system may be

provided.

Key-Words: - Archimedes Wind Turbine, Power Coefficient, Tip Speed Ratio, Angle of Attack

1 Introduction

Wind as a source of renewable energy receives a

great attention as an increasingly viable solution

to one of the most important issues of our time,

that is, pollution free electricity for sustainable

living. The continued dependence on depleting

fossil fuel sources or nuclear power has the

potential to wreck the world’s economy and

security. If the issue is not addressed with a

sense of urgency, then the havoc that the recent

nuclear power plant meltdown in Japan of 2011

or oil spills of the Gulf of Mexico of 2010

caused, will pale in comparison threatening

mankind’s very existence (Ahmed, 2013). Skea

(2014) described that the make-up of the EU’s

energy RD & D portfolio has changed to new

technologies such as wind and solar from fossil

energy conversion system. And he also

mentioned that the political environmental

change related on renewable energy leaded the

growth of the investment and R & D funding onthe renewable energy system. Bahaj et al. (2007)

described that small scale wind turbines installed

within the built environment is classified as

microgeneration technology and such turbines

may soon become a commercial reality in the

UK as a result of both advancements in

technology and new financial incentives

provided by the government. And they also

mentioned the proliferation of small scale wind

turbine for urban and suburban usage within near

future. Some researches into urban energy

generation showed that it is possible to predict

with a high degree of accuracy the expectedfinancial payback period for a typical domestic

household. A variety of wind turbines were

analyzed (Simic et al. 2013, Bortolini et al. 2014,

Arifujjaman et al. 2008).

Howell et al. would like to provide the

performance coefficient prediction on small

vertical axis wind turbine through experimental

and numerical study. They mentioned on

dynamic behavior of the over tip vortex as a

rotor blade rotating through each revolution.

These studies reported the effects of the bladegeometry on the power curve, the turbine’s rated

Ho S. Ji et al.

International Journal of Renewable Energy Sources

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power related to its swept area, the total

electricity production, and the pay-back period.

Herbert et al. reviewed the wind resources

assessment models, site selection models and

aerodynamic models including wake effect.

They also discussed that the differences exist in performance and reliability evaluation models,

various problems related to wind turbine

components (blade, gearbox, generator and

transformer) and grid for wind energy system.

Hirahara et al. studied on very small wind

turbine system with 500 mm as a diameter of

blades. Through their experimental study, they

mentioned that the maximum power coefficient

employed in their study showed approximately

40 % at 2.7 as a tip speed ratio. Quasim et al.

have studied for the power coefficient on cavityshape vane vertical axis wind turbine model

through wind tunnel experiment. Through their

experimental study, they mentioned that the

frame of vertical axis wind turbine may affect

the power coefficient. Ragheb et al. discussed

the Betz limit for horizontal and vertical axis

wind turbine systems. And they also mentioned

that the wind turbine must be designed to operate

at their optimal wind tip speed ratio in order to

extract as much power as possible from the wind

stream.

Even though there are lots of previous

research work on small wind turbine, there are

strong needs on the aerodynamic characteristics

including Power coefficient, Output power

according to the approaching wind condition

and blade feature. In this study, we would like

to provide the aerodynamic characteristics on

the 500 watt class Archimedes Spiral Wind

Turbine through two types of wind tunnel

employed in this study. And to provide thefundamental information on yawing system, the

aerodynamic characteristics with respect to the

angle of attack were also investigated through

large wind tunnel experiments. The results

employed in this study on aerodynamic

characteristics through wind tunnel experiments

may be applied for generator optimal design.

2 Experimental Setup and Methods

Figure 1 shows the experimental model ofArchimedes spiral wind turbine with 0.5kW

placed on atmospheric boundary layer wind

tunnel at Pusan National University. The open

suction type wind tunnel employed in this study

has 2m×2m as a cross-sectional area. The

experimental model was placed in the center of

the wind tunnel. The ball bearings wereinstalled in the frontward and backward of the

blade shaft. Wind turbine model employed in

this study was consisted with Archimedes spiral

wind blade, torque meter, powder brake and

rpm sensor. The torque meter was mechanically

assembled backward of Archimedes spiral wind

blade through main shaft of wind turbine model.

For the power coefficient calculation as a

function of tip speed ratio, Torque meter,

Powder Brake and RPM sensor was employed,

respectively.

Figure 1 Archimedes wind turbine model

placed in the wind tunnel (at PNU)

The Archimedes Spiral wind blade with

1.5m as a diameter was made of FRP resin and

Fiber Glass Sheet through by-layer process. The

thickness of the blade was approximately 3 mm

in the blade tip region and approximately morethan 5 mm in the center region for bonding

force with stainless steel shaft, respectively.

The rotating force control from powder

brake employed in this study can provide an

optimal performance of generator. And to

calculate the aerodynamic power, torque meter

was employed downstream of the blade model.

To prevent of the downstream wake flow

passing through the frame, the frames of wind

turbine model have airfoil shape.

In the case of high flow condition, to provide the stability of the spiral wind turbine

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model, the frame was tied up the wind tunnel

with damper for minimizing the vibration

between the wind turbine model and wind

tunnel. To investigate the approaching wind

speed, the Pitot tube was placed 2 m

downstream from the wind turbine model samewith the center of the experimental model.

3 Results and Discussions

Aerodynamic power production and power

coefficient from wind turbine is closely related

with the interaction between the rotor and the

incoming wind speed. The power coefficient of

wind turbine is defined as how efficiently the

wind turbine converts the energy from wind

into electricity. Tip speed ratio of wind turbineis an essential parameter to how efficient that

turbine will perform.

Equation (1) represents the definition on Tip

Speed Ratio.

TSR =R ×

(1)

Where R[m] is the radius of the wind blade,

ω[rad/s] is the angular velocity and [m/s] is

the approaching wind velocity.The input and output power through the

wind energy conversion can be represented as

equation (2) and (3), respectively.

= × (2)

=1

2 × × ×

3 (3)

Where, ρ means the air density, A means the

cross sectional dimension of wind turbine, means the wind speed, T means the torque, ω means the angular velocity of wind turbine,

respectively. As following to IEC-61400, ρ can be represented as 1.225 kg/m3.

According to the Betz Limit, the theoretical

maximum coefficient of power for any wind

turbines could not convert more than 59.3% of

the kinetic energy of the wind into mechanical

energy rotating the wind blade. Good wind

turbine generally fall in the 35~45% range of

electricity.

Figure 2 Generated Power as a function of the

Angular Velocity [from PNU Wind Tunnel]

Figure 2 shows the power curve with respect to

the angular velocity through wind tunnel

experiments. The experiments condition on the

approaching wind speed were controlled from 3

m/s to 11 m/s with step of 1 m/s. In the case of

3m/s as wind speed, even though the generated

power was not so sufficient, the generated

maximum aerodynamic power with

approximately 13.32 Watt through Archimedes

spiral wind blade can be observed at 8.08 as

angular velocity. The rotational power wascontrolled using powder brake and the

maximum aerodynamic power was observed at

16% as PWM (Pulse Width Modulation)

control value. In the case of 4m/s as wind speed,

the generated the maximum aerodynamic power

seems to be approximately 32.03 Watt at 12.26

as angular velocity. In this case, PWM control

value had 17%. In the case of 5m/s as wind

speed, the generated the maximum aerodynamic

power seems to be approximately 60.27 Watt at

12.44 as angular velocity. In this case, PWMcontrol value had 24%. In the case of 6m/s as

wind speed, the generated the maximum

aerodynamic power seems to be approximately

102.58 Watt at 20.34 as angular velocity. In this

case, PWM control value had 20%. In the case

of 7m/s as wind speed, the generated the

maximum aerodynamic power seems to be

approximately 168.96 Watt at 19.96 as angular

velocity. In this case, PWM control value had

25%. In the case of 8m/s as wind speed, the

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on Spiral Wind Blade generated the maximum

aerodynamic power seems to be approximately

250.31 Watt at 26.81 as angular velocity. In this

case, PWM control value had 25%. In the case

of 9m/s as wind speed, the generated themaximum aerodynamic power seems to be

approximately 339.10 Watt at 22.75 as angular

velocity. In this case, PWM control value had

30%. In the case of 10m/s as wind speed, the

generated the maximum aerodynamic power





power seems to be approximately 737.22 Watt

at 29.77 as angular velocity. In this case, PWM

control value had 35%.

Figure 3 shows the power coefficient as a

function of tip speed ratio with respect to the

wind speed change from 3m/s to 11m/s with

step as 1m/s. The maximum power coefficient

for each experimental condition from 3 m/s to

11 m/s as an approaching wind velocity can be

observed between 1.87 ~ 2.54. In the case of 11

m/s, the maximum power coefficient with

51.17 % can be observed. From this result, wecan consider that approximately 86.35% from

the optimal value of the performance coefficient

called as Betz Limit. From this figure, the

performance characteristics of the Archimedes

spiral wind turbine employed in this study

shows the similarity with Modern multibladeturbine. And the maximum power coefficient as

a function of the TSR shows the similar that of

Ideal Efficiency of Propeller-type turbine (J. N.

Libii, 2013). Table 1 represents the

experimental results through the Wind Tunnel

of Pusan National University with 2 m × 2 m as

a test section.

Figure 3 Power Coefficient as a function of Tip

Speed Ratio [from PNU Wind Tunnel]

Table 1 Aerodynamic Characteristics on Spiral Wind Blade

WindVelocity

MaximumAerodynamic

Power

MaximumPower

Coefficient[%]RPM

AngularVelocity

Tip Speed Ratio

3 m/s 13.3245.57 77.15

8.08 2.02

4 m/s 32.03 46.24 117.09 12.26 2.30

5 m/s 60.27 44.55 118.84 12.44 1.87

6 m/s 102.58 43.88 194.27 20.34 2.54

7 m/s 168.96 45.51 190.55 19.96 2.14

8 m/s 250.31 45.17 255.98 26.81 2.51

9 m/s 339.10 42.98 217.26 22.75 1.90

10 m/s 544.16 50.27 298.27 31.23 2.34

11 m/s 737.22 51.17 284.27 29.77 2.03

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To investigate the aerodynamic

characteristics on the Archimedes wind turbine

model according to the angle of attack change

and to compare the results through Pusan

National University Wind Tunnel by reducing

the blockage effect, the experimental modelwith turning plate was placed on the large wind

tunnel with 4 m × 2 m (width × height) as a test

section. The blade model for aerodynamic

characteristics investigation except turning plate

was same as previous experimental model.

Figure 4 shows the definition of angle of attack.

Figure 4 Definition of Angle of Attack

Figure 5 shows the power curve with

respect to the angular velocity through wind

tunnel experiments. The experiments condition

on the approaching wind speed were controlled

from 6 m/s to 12 m/s with step as 3 m/s. In the

case of 6m/s as wind speed, even though the

generated power was not so sufficient, thegenerated the maximum aerodynamic power

with approximately 123.80 Watt through

Archimedes spiral wind blade can be observed

at 19.44 as angular velocity. The rotational

power was controlled using powder brake and

the maximum aerodynamic power was observed

at 24% as PWM (Pulse Width Modulation)

control value.

In the case of 9m/s as wind speed, the

generated the maximum aerodynamic power





power seems to be approximately 915.94 Watt

at 37.95 as angular velocity. In this case, PWM

control value had 45%.

Figure 5 Aerodynamic Power as a function of

the Angular Velocity [CKP Wind Solutions]

4 Conclusion

To investigate the aerodynamic characteristics

on the 500 Watt class Archimedes spiral wind

turbine, proto-type experimental model was

employed through two types of wind tunnel.

The aerodynamic characteristics on the small

wind turbine with Archimedes spiral shape

through an experimental studies can be

summarized as follows;

(1) Through wind tunnel experiments on 2

types of wind tunnel, the higher output

power as a function of rotational velocity

than design specification was investigated

successfully. And also power coefficient as

a function of tip speed ratio with more than85% of Betz limit can be observed

successfully. From this sense, aerodynamic

conversion performance through

Archimedes spiral wind turbine model

employed in this study from wind energy

seems to have very higher efficiency

between the small wind turbine models.

The performance characteristics of the

Archimedes spiral wind turbine employed

in this study shows the similarity with

Modern multiblade turbine. And themaximum power coefficient as a function

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of the TSR shows the similar that of Ideal

Efficiency of Propeller-type turbine.

(2) Through the experiments on the angle of

attack change, the fundamental information

for the automatic yawing system design

may be provided. In the lower wind speedcondition similar with local wind condition

for urban such as between 3 ~ 6 m/s, the

highest output power and power coefficient

can be observed in the case of 0° wind

condition than angle of attack change.

From this sense, to provide the highest

efficiency to the household user, the

automatic yawing system for the

Archimedes wind turbine with easily facing

to the approaching wind direction seems to

be most effective. In the lower windcondition similar with urban normal wind

condition, the angle of attack can be

relatively estimated an important parameter

for the Archimedes spiral wind turbine

employed in this study.

Acknowledgments

This work was supported by the Korea Institute

of Energy Technology Evaluation and Planning

(KETEP), granted financial resource from theMinistry of Trade, Industry & Energy, Republic

of Korea. (G031711212 & 20153000000120)

And this was financially supported by the

Ministry of Trade, Industry and Energy

(MOTIE) and Korea Institute for Advancement

of Technology (KIAT) through the Promoting

Regional specialized Industry.

(G02A01190063301)

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